Cardiac Factors & Contractility
Increased cardiac mass can lead to ischemia, affecting Purkinje fibers and conduction.
Myocardial Infarction () results in muscle damage and reduced contractility.
Heart Rate & Contractility
Increased heart rate → Increased force of contraction.
Key Influences on Contractility:
Catecholamines (Epinephrine & Norepinephrine) → Stimulate calcium influx, increasing contractility.
Hypercalcemia (High Ca²⁺) → Stronger and prolonged contractions.
Role of Calcium in Cardiac Contraction
Calcium enters cardiac cells via action potentials.
Excess calcium prevents proper relaxation → Leads to sustained contractions.
Sympathetic stimulation increases calcium availability, enhancing contractility.
Effects of pH, CO₂, and Electrolytes on Contractility
Acidosis (↓ pH, ↑ H⁺ & CO₂) → Decreases contractility due to enzyme inhibition.
Alkalosis (↑ pH, ↓ H⁺ & CO₂) → Increases contractility but may cause arrhythmias.
Potassium (K⁺) & Contractility:
Hyperkalemia (High K⁺) → Weak contractions, risk of cardiac arrest.
Hypokalemia (Low K⁺) → Increases excitability, leading to arrhythmias.
Effects of Oxygen & Carbon Dioxide on Contractility
Increased O₂ → Enhances contractility.
Decreased O₂ (Hypoxia) → Weakens contractions, leading to heart failure.
CO₂ Retention (Hypercapnia) → Increases acidity, impairing myocardial contractility.
Note
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